The relationship between diet and exercise

This is a little lesson explaining the effects that nutrition and exercise have on each other.

I. Diet modulates weight.
II. Exercise modulates body composition.

1. Nutrition quality will improve how fast you lose or gain weight.
2. Exercise intensity will improve how fast your body composition changes.

Nutrition and exercise also have a big impact on health. Sleep also strongly impacts the results and health very strongly as well so quality of sleep is important.

Everything can be derived from these sets of statements. Let’s look at a couple of common examples.


1. You are obese and want to slim down.

Losing weight depends on nutrition. This is also why six packs are said to be “made in the kitchen.” Simply put: you need to eat less calories to drop weight.

  • Total daily energy expenditure (TDEE) is composed of basal metabolic rate (BMR) and calories burned from activities (ACTIVE). BMR is how many calories it takes to maintain body temperature and operate your essential organs like the brain, heart, and so on.

“Starvation mode” is a misnomer as if you eat extremely few calories your body will naturally drop weight, but the body can decrease metabolic rate by modulating thyroid hormones. This can also have some not-so-great effects on your organs.

Recommendation: It is best to stick with an energy deficit of somewhere between about 300-500 calories less than your TDEE per day, and your body will tend to drop .5-1 lbs per week or so.

Exercise is going to help modulate body composition while the pounds come off. For example, if you end up not exercising while on a caloric deficit, your body will indiscriminately drop muscle mass as well as fat mass. Eating enough protein and training will tend to prevent the loss of muscle mass during weight loss. Aim for 1g of protein per pound and 3x a week strength training while losing weight.


2. You are at a “healthy weight” for your height, but want to “tone up” and gain muscle mass while losing fat.

Toning is generally a misnomer built on the use of using “light weights” to tone. This is false.

Exercise here is the most important for any significant body composition change. Depending on the different types of exercise, your body may see fit to increase muscle mass and/or burn off excess fat mass (in conjunction with proper nutrition). Generally, you can lose fat and gain muscle at the same time, but how well you do this is predicated mainly on your percentage of body fat. If you have a higher body fat percentage, the easier it will be to lose weight due to much extra energy being available for the body to use to build muscle.

Diet is still very important because quality foods will produce faster body composition changes. This depends some on genetics (hence why some elite athletes can generally eat crap and get away with it), but even with good body composition changes with junky food may be at the expense of overall long term health.

Recommendation: Aim to get .7-1 g/lbs of protein and aim to only eat your TDEE in calories to maintain weight. Aim for at least 10 sets of exercises per muscle group to-failure or close to failure. Use heavy weights or difficult bodyweight exercises in the 5-15 repetition range.


3. The underweight person looking to “bulk up” with muscle.

Diet is the most important. This is a weight issue, and the person is looking to gain weight. Thus, they need to eat more.

This time around adding body mass will be variable according to the exercise (or lack thereof) because it affects body composition.

A. Lifting weights with a hypercaloric diet will tend to put on more muscle mass than fat.
B. Eating more without exercising tends to put on all fat as seen by the obesity rates in America.

Recommendation: Aim to get .7-1 g/lbs of protein for your targeted weight with an extra 500 calories a day. Aim for at least 10 sets of exercises per muscle group to-failure or close to failure. Use heavy weights or difficult bodyweight exercises in the 5-15 repetition range.


Onto more details…..

I. Regarding the quality of diet

Quality of diet is highly dependent on the genetics of the individual. Some people may be allergic to foods such as gluten or dairy, and consuming such food would be detrimental to overall health.

The one thing we can say is that improvements in the quality of diet directly leads to results in weight (maintenance, gain or loss) as well as quality of health. Since we literally are what we eat, if we take in junk food all the time our health is probably going to decline (even if we can’t see it on the outside), and the body will probably gain weight as junk food has a high caloric value.

Healthy bodies operate better mentally, physically, and emotionally so it is VERY important to get high quality nutrients.

Recommendations: avoid food allergens. Consume lots of fruits and vegetables. Aim for a moderate about of starchy foods like rice and potatoes. May need more starchy foods if you’re training hard. A fist size hunk of protein at most meals and extra if you need more. Supplements are to only supplement a healthy lifestyle. Whey can be useful if you need more protein.


II. Regarding the quality of exercise

High intensity or high power output exercise — heavy lifting, intervals, metabolic conditioning, etc. — tend to produce the fastest body composition changes. The stronger the stressors, the faster the body adapts. This is the SAID principle — specific adaptation to imposed demand. Of course, high intensity exercise can easily lead to overuse injuries, so listen to your body and be careful.

Damage to your muscles and their growth/adaptation require energy to repair which will be provided by through diet. If the energy need exceeds than of which the diet provides (hypocaloric diet for the obese & isocaloric diet for those who want to maintain weight), then the body tends to metabolize adipose tissue to supply the energy. In essence, our bodies adapt to stress. The higher the stress the bigger the adaptation. This is why higher intensity protocols such as weightlifting and HIIT get stronger adaptations to them than lower intensity such as cardio or very light weights.

The regulation of body composition operates according to the law of diminishing returns (aka logarithmic scale). This means that the improvements will be much greater the higher the body fat percentage & with less muscle mass, but much lower as the body fat percentage drops & with more muscle mass.

One fitness myth is that you cannot add muscle and lose fat at the same time; this is wrong and occurs frequently in obese individuals who are losing weight while doing high intensity exercise. However, as the BF% drops into the teens and single digits, it occurs much less if at all.


III. Regarding the reliance of diet and exercise to each other

In general, we would tend to say that overall improvement of weight and body composition is 80-85% diet and 15-20% exercise. This is because we are eating almost 21 times per week (maybe more) and only working out about 3-5 times a week.

These are the times that you will be affecting your weight and body composition, so they need to be used wisely. We often taking eating and exercising for granted, but if you want to make any significant weight or body composition changes these times must be taken seriously. Both quality and quantity matter.


This article was originally published August 19, 2009 on Eat Move Improve. Updated Dec 2016. 

Questions about articles may be addressed to the Overcoming Gravity reddit.

Author: Steven Low

Steven Low, author of Overcoming Gravity: A Systematic Approach to Gymnastics and Bodyweight Strength (Second Edition), is a former gymnast who has performed with and coached the exhibitional gymnastics troupe, Gymkana. Steven has a Bachelor of Science in Biochemistry from the University of Maryland College Park, and his Doctorate of Physical Therapy from the University of Maryland Baltimore. Steven is a Senior trainer for Dragon Door’s Progressive Calisthenics Certification (PCC). He has also spent thousands of hours independently researching the scientific foundations of health, fitness and nutrition and is able to provide many insights into practical care for injuries. His training is varied and intense with a focus on gymnastics, parkour, rock climbing, and sprinting.